The present invention relates to a flatbed system for flatbed scanners which consists of four optical units that can be moved relative to the image sensor to change the object distance and the image distance so as to adjust the resolution.
FIG. 1 shows the arrangement of the optical system 20 of a conventional flatbed scanner. This optical system 20 comprises a light source 101, a first reflector 102, a second reflector 103, a third reflector 104, a lens 105, and a CCD (charge-coupled device) 106. The reflectors 102-104, the lens 105 and the CCD 106 are fixed in place. When the optical scanner is operated, the optical system 20 is moved by a step motor through a transmission belt to scan the document. This optical system 20 is heavy, and therefore the power consumption problem is very serious during the operation of the optical scanner. Because the position of the optical system changes continuously during scanning, a flat cable is needed to transmit signals from the CCD 106 to the main board. In order to increase signal transmission speed, the frequency must be relatively increased. When the frequency is increased, the flat cable will cause a relatively serious radiation problem, and this radiation problem must be settled. Furthermore, because the flat cable is moved back and forth frequently, contact errors tend to occur.